Mercury (Hg) is a highly toxic compound and exposure at appreciable levels can lead to adverse health effects for people of all ages, including harm to the brain, heart, kidneys, lungs, and immune system. Mercury is naturally occurring but is also emitted from various human activities, such as burning fossil fuels and other industrial processes. For example, in the United States about 40% of the mercury introduced into the environment comes from coal-fired power plants.
In the United States and Canada, federal and state/provincial regulations have been implemented or are being considered to reduce mercury emissions, particularly from coal-fired power plants, steel mills, cement kilns, waste incinerators and boilers, industrial coal-fired boilers, and other coal combusting facilities. For example, the United States Environmental Protection Agency (U.S. EPA) has promulgated Mercury Air Toxics Standards (MATS), which would among other things require coal-fired power plants to capture approximately 90% of their mercury emissions beginning in 2015.
The leading technology for mercury control from coal-fired power plants is activated carbon injection. Activated carbon injection involves the injection of sorbents, particularly powdered activated carbon (“PAC”), into flue gas emitted by the boiler of a power plant. Powdered activated carbon is a porous carbonaceous material having a high surface area, which exposes significant amounts of beneficial chemically functional and catalytic reaction sites and which creates high adsorptive potential for many compounds, including capturing mercury from the flue gas. Activated carbon injection (“ACI”) technology has shown the potential to control mercury emissions in most coal-fired power plants, even those plants that may achieve some mercury control through control devices designed for other pollutants, such as wet or dry scrubbers used to control sulfur dioxide and acid gases.